Magnetron Sputter deposition of a 48-member cuprate superconductor library: Bi2Sr2YxCa1-xCu2Oy (0.5 <= x <= 1) linearly varying in steps of 0.01

Using magnetron sputtering, a spatial composition spread approach was applied successfully to obtain 48-member libraries of the Bi2Sr2YxCa1-xCu2Oy (0.5<= x <=1)cuprate superconducting system. The libraries of each system were deposited onto (100) single crystal MgO, mounted on a water cooled rotating table, using two targets: the antiferromagnetic insulator Bi2Sr2YCu2Oy (P=98 W RF) and the hole doped superconductor Bi2Sr2CaCu2Oy (P=44 W DC). A low chamber pressure of 0.81 mTorr argon is used to reduce scattering by the process gas. To minimize oxygen resputtering a substrate bias of -20 V was used as well as a process gas free of oxygen. A rapid thermal processor is used to post-anneal the amorphous deposited films. A step annealing regime was used, with a ramp rate of 5 degrees C/s for heating and cooling, with a first plateau at 780 C held for 200 s, and a second at 875 C held for 480 s. X-ray diffraction reveals that the films develop crystalline order with the c-axis lattice parameter contracting linearly from 30.55 Angstroms (x=0.5) to 30.24 Angstroms (x=1.0) with increasing Y-content, consistent with bulk values. The crystallized films are polycrystalline, developing preferred orientation (c-axis parallel to the substrate) for thinner members of the library. There is a change of 0.01 in doping per library member which will enable further studies to densely map phase space.Comment: 4 pages, 6 figures, submitted Jan. 31, 2007: Applied Surface Science - Proceedings of the 4th International Workshop on Combinatorial Materials Science & Technology, San Juan, Puerto Ric

Magnetotransport near a quantum critical point in a simple metal

We use geometric considerations to study transport properties, such as the conductivity and Hall coefficient, near the onset of a nesting-driven spin density wave in a simple metal. In particular, motivated by recent experiments on vanadium-doped chromium, we study the variation of transport coefficients with the onset of magnetism within a mean-field treatment of a model that contains nearly nested electron and hole Fermi surfaces. We show that most transport coefficients display a leading dependence that is linear in the energy gap. The coefficient of the linear term, though, can be small. In particular, we find that the Hall conductivity $\sigma_{xy}$ is essentially unchanged, due to electron-hole compensation, as the system goes through the quantum critical point. This conclusion extends a similar observation we made earlier for the case of completely flat Fermi surfaces to the immediate vicinity of the quantum critical point where nesting is present but not perfect.Comment: 11 pages revtex, 4 figure

Identification of volatiles generated by potato tubers (Solanum tuberosum CV : Maris Piper) infected by erwinia carotovora, bacillus polymyxa and arthrobacter sp

Bacteria were isolated from internal tissues of surface sterilized healthy tubers of Solanum tuberosum cv. Maris Piper (8 different isolates) and from tubers inoculated with Erwinia carotovora ssp. carotovora showing soft-rot symptoms (3 different isolates), and identified by fatty acid profiling. Bacillus polymyxa and an Arthrobacter sp. were isolated from both sources, E. carotovora only from the soft-rotted tubers. The volatile organic compounds (VOCs) generated by tubers inoculated with E. carotovora, B. polymyxa and the Arthrobacter sp. were identified. Inoculated tubers of cv. Maris Piper were incubated under controlled humidity (95% relative humidity) and temperature (10°C) to simulate typical storage conditions. B. polymyxa and Arthrobacter sp. did not cause symptoms, whilst E. carotovora caused limited soft-rot infections after 4 weeks at the low temperatures typically associated with potatoes in storage. The VOCs released to the headspace around these tubers were collected using an adsorbent system and analysed by Gas Chromatography-Mass Spectrometry (GC-MS). Twenty-two volatiles unique to E. carotovora infection of potato tubers were found,) including 10 alkanes, four alkenes, two aldehydes, one sulphide, one ketone, one alcohol, one aromatic, one acid and one heterocyclic compound. B. polymyxa generated three unique volatiles: N,N-dimethylformamide, 1-pentadecene and 1-hexadecane. Only one volatile, 2,3-dihydrofuran, was unique to the Arthrobacter infection. Production of volatile nitrogen species from E. carotovora-infected tubers increased with time, whereas none were detected in the headspace above uninfected tubers. Further analysis using a modified GC-MS method established that ammonia, trimethylamine and several volatile sulphides were evolved from tubers infected by E. carotovora. No specific volatile was useful as a marker associated with any of the three bacterial species but in the case of E. carotovora-infected potato tubers a significant increase in the volume of compounds evolved was clearly observed. The results are discussed in relation to the use of sensors to detect VOCs evolved from infected tubers in order to provide an early warning system for the control of soft rot in potato store

Kochen-Specker Sets and Generalized Orthoarguesian Equations

Every set (finite or infinite) of quantum vectors (states) satisfies generalized orthoarguesian equations ($n$OA). We consider two 3-dim Kochen-Specker (KS) sets of vectors and show how each of them should be represented by means of a Hasse diagram---a lattice, an algebra of subspaces of a Hilbert space--that contains rays and planes determined by the vectors so as to satisfy $n$OA. That also shows why they cannot be represented by a special kind of Hasse diagram called a Greechie diagram, as has been erroneously done in the literature. One of the KS sets (Peres') is an example of a lattice in which 6OA pass and 7OA fails, and that closes an open question of whether the 7oa class of lattices properly contains the 6oa class. This result is important because it provides additional evidence that our previously given proof of noa =< (n+1)oa can be extended to proper inclusion noa < (n+1)oa and that nOA form an infinite sequence of successively stronger equations.Comment: 16 pages and 5 figure

Electron Spin Relaxation in a Semiconductor Quantum Well

A fully microscopic theory of electron spin relaxation by the D'yakonov-Perel' type spin-orbit coupling is developed for a semiconductor quantum well with a magnetic field applied in the growth direction of the well. We derive the Bloch equations for an electron spin in the well and define microscopic expressions for the spin relaxation times. The dependencies of the electron spin relaxation rate on the lowest quantum well subband energy, magnetic field and temperature are analyzed.Comment: Revised version as will appear in Physical Review

Situating commercialization of assisted reproduction in its socio-political context: a critical interpretive synthesis.

BACKGROUND: In many countries, ART service provision is a commercial enterprise. This has benefits, for example, creating efficiencies and economies of scale, but there are also concerns that financial imperatives can negatively impact patient care. The commercialization of ART is often conceptualized as being driven solely by the financial interests of companies and clinicians, but there are in fact many complex and intersecting socio-political demands for ART that have led to, sustain and shape the industry. OBJECTIVE AND RATIONALE: To use the academic and policy discourse on the commercialization of ART to build a theoretical model of factors that influence demand for ART services in high-income countries in order to inform potential policy responses. SEARCH METHODS: We searched electronic databases for journal articles (including Web of Science, Scopus, PubMed) and websites for grey literature, carried out reference chaining and searched key journals (including Human Reproduction, Fertility and Sterility). The terms used to guide these searches were 'assisted reproductive technology' OR 'in vitro fertilization' AND 'commerce' OR 'commercialisation' OR 'industry' OR 'market'. The search was limited to the English language and included articles published between 2010 and 2020. We used an established method of critical interpretive synthesis (CIS) to build a theoretical model of factors that influence demand for ART services in high-income countries. We developed initial themes from a broad review of the literature followed by iterative theoretical sampling of academic and grey literatures to further refine these themes. OUTCOMES: According to contemporary academic and broader socio-political discourse, the demand for ART has arisen, expanded and evolved in response to a number of intersecting forces. Economic imperatives to create sustainable national workforces, changing gender roles and concerns about the preservation of genetic, national/ethnic and role-related identities have all created demand for ART in both public and private sectors. The prominence given to reproductive autonomy and patient-centred care has created opportunities to (re)define what constitutes appropriate care and, therefore, what services should be offered. All of this is happening in the context of technological developments that provide an increasing range of reproductive choices and entrench the framing of infertility as a disease requiring medical intervention. These socio-political drivers of demand for ART can be broadly organized into four theoretical categories, namely security, identity, individualization and technocratization. LIMITATIONS REASONS FOR CAUTION: The primary limitation is that the interpretive process is ultimately subjective, and so alternative interpretations of the data are possible. WIDER IMPLICATIONS: Development of policy related to commercial activity in ART needs to account for the broad range of factors influencing demand for ART, to which commercial ART clinics are responding and within which they are embedded. STUDY FUNDING/COMPETING INTERESTS: This work was supported by a National Health and Medical Research Council Ideas Grant (APP1181401). All authors declare that they have no conflict of interest in relation to this work.Narcyz Ghinea, Miriam Wiersma, Ainsley J. Newson, Catherine Walby, Robert J. Norman, and Wendy Lipwort

Neutron background in large-scale xenon detectors for dark matter searches

Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (alpha,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of $10^{-9}-10^{-10}$ pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector.Comment: 35 pages, 13 figures, 2 tables, accepted for publication in Astroparticle Physic

Possible isotope effect on the resonance peak formation in high-Tc_c cuprates

Starting from the three-band $p-d$ Hubbard Hamiltonian we derive an effective $t-J$ model including electron-phonon interaction of quasiparticles with optical phonons. Within the effective Hamiltonian we analyze the influence of electronic correlations and electron-phonon interaction on the dynamical spin susceptibility in layered cuprates. We find a huge isotope effect on the resonance peak in the magnetic spin susceptibility, ${Im}\chi({\bf q},\omega)$, seen by inelastic neutron scattering. It results from both the electron-phonon coupling and the electronic correlation effects taken into account beyond random phase approximation(RPA) scheme. We find at optimal doping the isotope coeffiecient $\alpha_{res} \approx 0.35$ which can be further tested experimentally.Comment: revised version, new figure is added. Phys. Rev. B 69, 0945XX (2004); in pres

Interplay among critical temperature, hole content, and pressure in the cuprate superconductors

Within a BCS-type mean-field approach to the extended Hubbard model, a nontrivial dependence of T_c on the hole content per unit CuO_2 is recovered, in good agreement with the celebrated non-monotonic universal behaviour at normal pressure. Evaluation of T_c at higher pressures is then made possible by the introduction of an explicit dependence of the tight-binding band and of the carrier concentration on pressure P. Comparison with the known experimental data for underdoped Bi2212 allows to single out an `intrinsic' contribution to d T_c / d P from that due to the carrier concentration, and provides a remarkable estimate of the dependence of the inter-site coupling strength on the lattice scale.Comment: REVTeX 8 pages, including 5 embedded PostScript figures; other required macros included; to be published in Phys. Rev. B (vol. 54

Effect of an Electron-phonon Interaction on the One-electron Spectral Weight of a d-wave Superconductor

We analyze the effects of an electron-phonon interaction on the one-electron spectral weight A(k,omega) of a d_{x^2-y^2} superconductor. We study the case of an Einstein phonon mode with various momentum-dependent electron-phonon couplings and compare the structure produced in A(k,omega) with that obtained from coupling to the magnetic pi-resonant mode. We find that if the strength of the interactions are adjusted to give the same renormalization at the nodal point, the differences in A(k,omega) are generally small but possibly observable near k=(pi,0).Comment: 10 pages, 14 figures (color versions of Figs. 2,4,10,11,12 available upon request